Upgrade to 8.0.2 - Mobile Sync with Acer Iconia not working

We recently upgraded from 7.2.0 to 8.0.2.
In Version 7.2.0 all synchronisation with mobile devices (Smartphones: iPhone, HTC, Motorola, Samsung; Tablets: iPad, Acer Iconia) work fine.
In 8.0.2 synchronisation works for all devices except "Acer Iconia". On the tablet it shows that the synchronisation is OK. But there is no synchronisation. On the calender it shows "Kein Kalender" (no calendar). Zimbra server is hosted by our service provider. Actually we have no access to any log files.
Any idea?